1. Field of the Invention
The present invention relates to a toner for use in electrophotography, and more particularly to the shape of a polymerized toner.
2. Discussion of the Background
A polymerized toner is prepared by solidifying a liquid droplet in a liquid emulsion or liquid suspension, i.e., oil in water, and alternatively dispersing and agglutinating particles and melting or softening the agglutinated particles to be associated in an aqueous medium. Formed through a liquid status, the particles tend to be spherical due to oil phase surface tension.
However, a spherical toner is more difficult than a pulverized toner to clean with a blade, which is currently a major cleaning device used in the industry, because the spherical toner is thought to have less edges than the pulverized toner. This problem is widely known in the electrophotographic field as disclosed in Japanese Published Unexamined Applications Nos. 2002-287400, 2003-058009, 2004-226663 and 2005-037923.
The more deformed the spherical toner, the more edges the toner has and the easier it is to clean. However, the more deformed, the more technically difficult and the lower the image quality. Therefore, the cleanable minimum deformity is an important subject in the electrophotographic field.
On the other hand, global environmental protection is more desired recently, and an energy-saving toner is required even in electrophotography.
A polymerized toner has a minimum fixable temperature of from 140 to 150° C. at lowest, and a fixable temperature width, i.e., hot offset temperature minus minimum fixable temperature, of from 50 to 60° C. at most.
Many toners prepared by non-pulverization methods using a dispersion or a solution of a resin or its precursor are known. For example, conventional polymerized toners prepared not only by a dispersion polymerization method disclosed in Japanese Published Unexamined Patent Application No. 63-297402 are just spherical, not semispherical having plural dents, and thus do not have sufficient cleanability. Japanese Published Unexamined Patent Application No. 2005-37923 discloses a toner having the shape of a rugby ball, which has sufficient cleanability, but produces images having quality worse than those produced by use of a spherical toner. In addition, to have the shape of a rugby ball, an extra process is necessitated.
Because of these reasons, a need exists for a toner having good cleanability and low-temperature fixability, and producing quality images.